'X' ENCON,TRO NACIONAL DE FISICA DA MATERIA CONDENSADA

XX ENFMC - Resumos 31
IDENTIFICATION OF TISSUE
ACTIVATION DURING ATRIAL FLUTTER
BY MAGNETIC MEANS USING A
CELLULAR AUTOMATA MODEL
E. COSTA MONTEIRO, L. C. MIRANDA, P. COSTA
RIBEIRO
Departatnento de Fisica, Pontificia Universidade Catolica
do Rio de Janeiro, Caisa Postal 38071, Cep 22452-970, RJ
The non-invasive identification of heart tissue activation
during periodic tachyarrhythmias like atrial flutter
is a challenge for its clinical assessment. The conventional
surface ECG tracing does not allow to determine
the exact sequence of cardiac electrical events. Otherwise,
through magnetic means, a non-invasive assessment
of primary currents generated in the heart tissue
can be achieved, since most magnetic field detected
is produced by the primary currents propagating
in the heart. A discrete cellular automation computer
model was applied to simulate the excitation wave
propagation characteristic of the fundamental mechanisms
of atrial flutter arrhythmia. The magnetic field
produced by the different simulated activation models
has been calculated. As the atrial myocardium behaves
electrophysiologically as a two-dimensional surface,
a bidimensional cellular automata simulation is appropriate
for the study of atrial flutter mechanisms. Atrial
flutter is most predominantly associated to a reentrant
excitation and less frequently to a rapid ectopic focus.
Reentry may result from anatomical or functional mechanisms.
The anatomical one presents a central anatomical
conducting obstacle (the ring model). Contrasting,
the functional circuits are defined by the electrophysiological
properties of the cardiac tissue (the spiral
model). These different propagation mechanisms have
been simulated. The signal was computed for different
positions in a plane parallel to the simulated grid for
each propagation model. Isoamplitude maps were configured
showing a line of minimum amplitude for the linear
prOpagation of an ectopic focus; the characteristic
single point of minimum amplitude for the circus movement;
and for the spiral model a composite of both. For
this latter, the presence of multiple radial lines of minimum
spreading from the central minimum amplitude
could demonstrate the existence of multiple preferential
courses of activation toward the grid borders. Therefore,
the different computational images obtained could
identify the various tissue activation associated to the
mechanisms of atrial flutter arrhythmia.
Distinction Between Reentry Circuit and
Ectopic Focus Mechanisms of Arrhythmias
Through Simulated and Experimental
Magnetic Studies
E. COSTA MONTEIRO, L. C. MIRANDA, A. C.
BRUNO, P. COSTA RIBEIRO
Departarnento de Fisica, Pontificia Universidade Catolica
do Rio de Janeiro, Cairo Postal 38071, Cep 22.452-970, RJ
The exact electrical mechanism associated with sustained
arrhythmias like cardiac flutter and fibrillation is
still unclear. Most evidence points toward a reentry
path, although the automatic disorder due to an ectopic
focus is still considered. To evaluate the possibility
of distinguishing between both activation mechanisms,
synthetic and experimental studies are presented. The
experimental model to evaluate the magnetic field generated
by an ectopic focus was the isolated rabbit heart
preparation maintained in sinusal rhythm. The propagation
generated by an ectopic focus is similar to the
activation of the normal focus displaced on atrial tissue.
For the experimental circus movement study, atrial flutter
was induced in isolated rabbit hearts. The experimental
procedures were performed using isolated rabbit
hearts maintained in perfusion (Langerdorf's system).
Magnetic measurements were carried out with a onechannel
rf-SQUID magnetometer coupled to a second
order gradiometer. The signals were digitally processed
to configure the isofield and isoamplitude maps.
The synthetic study to evaluate the experimental results
was done using a bidimensional cellular automata
computer model to simulate the different tissue activation
mechanisms. The program consists of a grid of
hexagonal cells considering the recovery time of the simulated
cell with its spatial dispersion. Isofield maps
have shown a dipolar configuration rotating in both experimental
atrial flutter and circus movement simulation.
They presented also the same behavior for the
isoamplitude maps configuration, a single point of minimum
oscillatory field. Constant direction of activation
in the isofield map and a line of minimum oscillatory
field instead of a single point in the isoamplitude map
was observed for both experimental and synthetic linear
propagation. This results show the potentiality of the
non-invasive magnetocardiography to distinct between
circus movement and focal impulse propagation associated
to cardiac arrhythmias with its clear implications
in electrophysiologic and clinical diagnostic studies.